1. Field of the Invention
This invention relates to a forced convection heating furnace for heating glass sheets and also relates to a method for heating glass sheets.
2. Background Art
Forced convection furnaces are used to heat glass sheets in preparation for processing such as forming, tempering, heat strengthening, annealing, and coating, etc. Such prior art forced convection furnaces for heating glass sheets are disclosed by the United States patents of Kenneth R. Kormanyos: U.S. Pat. Nos. 5,669,954; 5,672,191; 5,735,924; 5,746,799; 5,762,677; 5,792,232; and 6,045,358. In the Kormanyos patents, the glass sheets are conveyed on a roll conveyor during the heating which is performed by lower and upper sets of hot gas hot gas distributor heads that supply upwardly and downwardly directed pressurized hot gas flows to the lower and upper surfaces of the conveyed glass sheets. An associated lower hot gas distributor head is located between each pair of adjacent conveyor rolls, such that the spent quenching gas must flow downwardly between the conveyor rolls and the hot gas distributor head. Furthermore, any broken glass that is lodged between the conveyor rolls and the lower hot gas distributor heads must be removed before commencing further heating of the glass sheets.
The United States patents of Troy R. Lewandowski U.S. Pat. Nos. 6,050,814 and 6,155,822 disclose forced convection heating of glass sheets conveyed on a roll conveyor wherein lower hot gas distributor heads provide upwardly directed hot gas flows both upstream and downstream of alternate conveyor rolls in a manner that provides sufficient room for the spent gas flows to move downwardly after impingement with the glass sheet being heated.
In both the above mentioned Kormanyos and Lewandowski patents, the heated gas is supplied by mixing spent recirculating gas with the heated products of combustion from gas burners mounted on one side wall of the furnace, such that the spent recirculating gas flows to the one side wall. Within the furnace heating chamber, the temperature can be lower adjacent the side wall to which the spent recirculating gas flows because it has a lower temperature than the heated gas upon distribution prior to the impingement with the conveyed glass sheets.
An object of the present invention is to provide an improved furnace for heating glass sheets.
In carrying out the above object, the furnace for heating glass sheets in accordance with the invention includes a housing having a pair of side walls, a floor and a ceiling that cooperate to define a heating chamber. A roll conveyor of the furnace conveys glass sheets through the heating chamber along a direction of conveyance. A forced convection heater of the furnace is located within the housing and includes a gas burner assembly generally adjacent one of the housing side walls. The gas burner assembly includes an outlet through which heated products of combustion from the gas burner assembly are supplied to the heating chamber at a location intermediate the housing side walls. The forced convection heater also includes a hot gas distributor located within the housing generally adjacent the other side wall and including an inlet that is spaced from the outlet of the gas burner assembly intermediate the housing side walls. The hot gas distributor has a suction fan for drawing the heated products of combustion from the outlet of the gas burner assembly together with spent quenching gas in the heating chamber into the hot gas distributor through its inlet for mixing to provide heated gas. The hot gas distributor also has distribution openings through which the mixed heated gas is distributed to the conveyed glass sheets on the roll conveyor to provide heating of the glass sheets.
The construction of the furnace and its forced convection heater provides a generally uniform temperature in the heating chamber between the housing side walls. More specifically, the actual construction of the furnace includes a plurality of the forced convection heaters positioned along the direction of conveyance both below and above the roll conveyor to provide upwardly and downwardly directed heated gas flows to the conveyed glass sheets on the roll conveyor to provide the heating of the glass sheets.
The furnace preferably has the midpoint between the side walls of the housing located between the outlet of the gas burner assembly and the inlet of the hot gas distributor. A delivery tube of the gas burner assembly has an outer end mounted by the one side wall and the gas burner assembly has a gas burner mounted by the one side wall within the delivery tube adjacent its mounted outer end. An inner end of the delivery tube defines the outlet of the gas burner assembly through which the heated products of combustion from the gas burner are supplied with, as mentioned above, a midpoint between the side walls of the housing being located between the outlet of the gas burner assembly and the inlet of the hot gas distributor.
The outlet of the gas burner assembly in one construction includes an adjustable damper for controlling the flow of heated products of combustion into the heating chamber.
In another construction, the gas burner assembly includes a delivery tube, the gas burner assembly has a gas burner that is received within the delivery tube, the delivery tube includes an inner end defining the outlet of the gas burner assembly, the delivery tube includes openings through which a portion of the heated products of combustion from the gas burner flow outwardly without passing through the outlet at the inner end of the delivery tube, and the outlet of the gas burner assembly includes a damper that is adjustable to control the relative amounts of the heated products of combustion that flow through the openings of the delivery tube and through the outlet at the inner end of the delivery tube. This embodiment of the furnace also includes an enclosure in which the delivery tube with the gas burner therein is received. The inner end of the delivery tube opens outwardly through the enclosure into the heating chamber adjacent the inlet of the hot gas distributor. The enclosure has openings through which the heated products of combustion that pass outwardly through the openings of the delivery tube can pass outwardly from the enclosure into the heating chamber. This embodiment also has the outlet of the gas burner assembly including the damper that is adjustable to control the relative amounts of the heated products of combustion that flow through the openings of the delivery tube and through the outlet at the inner end of the delivery tube and also has the midpoint between the side walls of the housing located between the outlet of the gas burner assembly and the inlet of the hot gas distributor.
Another object of the present invention is to provide an improved method for heating glass sheets.
In carrying out the immediately preceding object, the method for heating glass sheets in accordance with the invention is performed by conveying glass sheets on a roll conveyor along a direction of conveyance within a heating chamber cooperatively defined by side walls, a floor and a ceiling of a housing. Heated products of combustion are supplied from a gas burner assembly mounted adjacent one side wall of the housing through an outlet of the gas burner assembly into the heated chamber at a location intermediate the housing side walls. The heated products of combustion are drawn from the outlet of the gas burner assembly together with spent recirculating gas in the heating chamber into a hot gas distributor through an inlet thereof for mixing to provide heated gas. The mixed heated gas is distributed to the conveyed glass sheets on the roll conveyor to provide heating of the glass sheets.
The method for heating glass sheets in accordance with the invention is actually performed with the heated products of combustion supplied from a plurality of gas burner assemblies spaced along the direction of conveyance both above and below the roll conveyor. The heated products of combustion along with spent recirculating gas are drawn from the outlets of the gas burner assemblies into inlets of associated hot gas distributors spaced along the direction of conveyance both below and above the roll conveyor for mixing to provide heated gas. This mixed heated gas is distributed both upwardly and downwardly to the conveyed glass sheets on the roll conveyor to provide heating of the glass sheets.
The method for heating glass sheets has the heated products of combustion preferably supplied from the outlet of the gas burner assembly to the heating chamber at a midpoint between the side walls of the housing.
The glass sheet heating method may also use an adjustable damper to control the flow of heated products of combustion through the outlet of the gas burner assembly.
The objects, features and advantages of the present invention are readily apparent from the following detailed description of the invention when taken in connection with the accompanying drawings.